Process for the production of fibrous cellulose nitro-acetate soluble in acetone



Patented June 12, 1934 PROCESS FOR THE PRODUCTION OF FIEROUS CELLULOSE NITRO ACETATE SOLUBLE IN ACETONE Harry Le B. Gray, Rochester, N. Y., assignor to Eastman Kodak Company, Rochester, N. Y., a corporation cf New York No Drawing. Application August 23, 1930, Serial No. 477,466

2 Claims.

This invention relates to a process for the production of fibrous cellulose nitro acetate soluble in acetone.

The processes usually employed in the commer- 5 cial manufacture of cellulose acetate produce a chloroform soluble product which is soluble in the acetylating bath. To render this product soluble in acetone, it may be held for a sufiicient period of time in the reaction bath until the desired solubility is attained. Generally, however, some chemical is added to the esterifying bath to destroy the action of the acetic anhydride which may be present therein and to likewise hydrolyze the cellulose acetate. There are a great number of processes for eifecting this result.

Manufacturers of cellulose acetate have realized for some time that if a commercial process could be devised to prepare cellulose acetate in the fibrous form and soluble in acetone, considerable economies in the cost of producing this ester would result. In the patents and literature there are processes described for the hydrolysis of chloroform soluble fibrous cellulose acetate but none of them have proven to be sufiiciently economical nor the product of sufiiciently good quality for commercial application.

An object of the present invention is to provide a process for obtaining fibrous cellulose nitro acetate, soluble in acetone. Another object of this invention is to provide a process for obtaining acetone soluble fibrous cellulose nitro acetate wherein the acetone solubility. is effected by a gaseous medium. Other objects will hereinafter appear.

I have found that the oxides of nitrogen and especially nitrogen dioxide (N02) and its dimer (N204) when passed into a partially acetylated fibrous cellulose acetate saturated with the acetylating agent and held in contact therewith will for instance, change the solubility of the product, which would otherwise result, from chloroform solubility to a solubility in acetone. I am inclined to believe that in this case there is a slight interaction between the partially acetylated cellulose acetate and the oxide of nitrogen; the resulting product may contain in the order of 1 to 5 per cent nitrogen or in some instances more. The presence of so small an amount of nitrogen, however, does not in any way decrease the quality of the film, made from the thus treated ester, but in fact appears to give to films of such cellulose acetate improved qualities which the non-nitrogen containing films do not have.

The advantages of such a film and another method for its preparation is described in the copending application of Staud, Webber and Van Dyke, Serial No. 378,557.

In conducting my process, I have found that after the cellulosic material has been. partially g0; esterified in fibrous form in a suitable acetylating bath such as that described in the U. 5. Patent 1,690,632, of H. Le B. Gray and C. J. Stand, it is advisable to press out of the cellulose acetate the majority of the residual acetic anhydride before treatment with the oxides of nitrogen which it contains. Herein lies one of the economical advantages of the esterification of cellulose in the fibrous form as the reaction products are not diluted by this process and can be economically recovered, while on the other hand if the cellulose acetate be produced in the dope form, i. e. in solution, the reaction mass is usually immersed in a large volume of water in order to precipitate out the cellulose acetate, thereby diluting any acetic anhydride and acetic acid present and making more difficult the recovery of the latter. After the removal of the reaction mixture from the partially esterified fibrous cellulose acetate, the lat- 8Q ter is placed in a suitable container and therein impregnated with an oxide of nitrogen. This is best carried out in a suitable type autoclave, a vacuum being drawn on the container prior to the admission of the oxide of nitrogen.

Care must be exercised during the first stages of the reaction that the nitrogen dioxide or other oxide of nitrogen be not added too rapidly to the fibrous cellulose acetate, as this develops considerable heat with the resultant degradation of the final product. It is likewise advisable to have a jacketed container means of which the temperatures of the reaction mixture may be readily controlled. In' some instances it will be found advantageous to allow the oxide of nitrogen to develop a considerable pressure within the container thereby decreasing the time of the reaction but I have found this not generally necessary.

I shall now give a preferred example for carrying out my invention, although it will be understood that the process has many possible modifications and possible substitutions of equivalents for the various ingredients found therein and by so doing there will be no departure from the scope of the present invention unless such changes: be not included in the appended claims.

Example 1.Cellulosic materials such as purified cotton linters, are first thoroughly mixed with the acetylating bath. This is best elfected by immersing and acetylating the fibers such as 100 parts by weight of cotton linters, for approximately five minutes, in an esterifying bath containing, for example, approximately 1,400 parts by weight of acetic anhydride (94% strength) and 0.9 parts of sulphuric acid (98% strength) and 0.9 parts of phosphoric acid (35% strength). As the quantity of anhydride herein given is in excess or" that required for the acetylation of 100 parts of cotton, the saturated cotton fibres after about five minutes acetylation with agitation are pressed until the mass amounts to approximately 320 parts, which corresponds to about 190 parts of cellulose, 220 parts of anhydride, and the retained catalyst, approximately .25? of a part. At this point, the mixture has much the appearance of the original cellulose, although slightly moist with the acetic anhychide, and containing a small percentage of acetyl.

This product may now be placed in an autoclave and im regnated with an oxide of nitrogen such as nitrogen dioxide-the nitrogen dioxide being added slowly in order that the increase in temperature resulting from its addition be not too great, th reby preventing unnecessary degradation of the cellulose ester. The cellulose acetate is held in contact with the oxide of nitrogen until the desired solubility in acetone is attained, this point being determined by test of a sample in the usual way. In order to effect a more uniform and rapid reaction, we have found that upon the addition of the partially esterified cellulose acetate to an autoclave or similar container, such a result can be obtained by drawing a strong vacuum on the container, thus removing the greater proportion o1": occluded gases in the fibrous cellulose ester, then passing the oxide of nitrogen into the autoclave, thus completely filling the interstices in the cellular material.

In some instances it may be even advisable, after the heat evolved by the initial introduction of the oxide of nitrogen has been disseminated, to pump the nitrogen oxide into the autoclave until a suitable pressure has been developed, thereby increasing the velocity of the reaction. Under ordinary conditions without the added pressure it requires approximately 3-4 weeks for changing the solubility of the partially esterifled fibrous acetate to a cellulose ni p acetate soluble in acetone when the reaction is controlled at room temperature.

Example 2.50 grams of cotton linters were treated with 70 c. c. of 529% acetic anhydride and 1 c. c. of 1:1 mixed sulfuric-phosphoric catalyst (95%) for five minutes and then pressed down to a weight of 175 grams. This was then transferred to a suitable flask. The flask and contents were cooled down to below 18 C. and a stream of N02 passed into the flask keeping the temperature below 30 C. at all times and stirring the cotton almost constantly. This resulted in a fine fluffy product free from lumps. After the danger from temperature increase was passed, the flask was put on the agitating machine and rotated at room temperature. After 3 to 4 weeks the product gave a fairly clear viscous solution in acetone. It was washed with CCl-l, alcohol and then with water to neutrality. Analysis: Nitrogen 5%, acetyl 41.8%, M. P. 204 C.

While I have described a process of producing cellulose nitro-acetate from partially acetylated cellulose it will be understood that my invention is somewhat broader in scope inasmuch as a nitrocellulose ester of any of the lower fatty acids may be produced by partially esterifying cellulose by means of a suitable catalyst and the anhydride of the lower fatty acid, the ester of which it is desired to produce, and then with the fibrous partially esterified cellulose acylate still saturated with the esterification mixturetreating the product with an oxide of nitrogen, such as nitrogen dioxide, all as will be apparent from the above examples. Of course, the nitro-formate is hardly feasible and the higher fatty acids are too slow in their reaction so that it may be stated that the acylates corresponding to fatty acids having from two to six carbon atoms in the acyl group are those intended to be included in the phrase cellulose esters of the lower fatty acids.

From a consideration of the above description it will be realized that any process for the treatment of partially acetylated fibrous cellulose acetate or other partially esterified cellulosic ester of a lower fatty acid to give a product having solubility characteristics differing from those which would be obtained by direct acetylation or esterification will come within the scope or" this invention, if such a process be conducted with the aid of an oxide of nitrogen.

What I claim as my invention and desire to be secured by Letters Patent of the United States is:

1. A process for preparing acetone soluble fibrous cellulose nitro acetate which comprises acetylating partially acetylated fibrous cellulose acetate in the presence of a substantial amount of nitrogen dioxide.

2. A process for preparing acetone-soluble fibrous cellulose nitro-acetate which comprises treating 1 part of cellulose with approximately l l parts of acetic anhydride and a small amount of catalyst for a short time, pressing the mass and then impregnating the same with nitrogen dioxide and allowing the mass to react until an acetone-soluble product is obtained.

HARRY LE B. GRAY.

m loo CERTIFICATE OF CORRECTION.

Patent No. l,962, 345. June 12, 1934.

HARRY Le B. GRAY.

It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction as follows: Page 2, line 55. for "70" read 700; and that the said Letters Patent should be read with this correction therein that the same may conform to the record of the case in the Patent Office.

Signed and sealed this 7th day of August, A. D. 1934.

Leslie Frazer (Seal) Acting Commissioner of, Patents. 

